DVD is generally a technology designed to replace current compact disks or CD-ROMs. There are generally two types of DVDs. The first type is constructed very similarly to current CD-ROMs with two significant distinctions. The first distinction between current CD-ROMs and DVDs involves how the data is represented. Although, data is represented on both the DVD and the CD-ROM as pits, the pits on the DVD are about one half the size of the pits on the CD-ROM (0.4 microns versus 0.83 microns). The second distinction between current CD-ROMs and DVDs involves the placement of the data or the track size. On the DVD, the tracks are much closer than that of the current CD-ROMs (0.74 microns versus 1.6 microns). These two distinctions alone enable the DVD to store nearly seven times the capacity of current CD-ROMs (4.7 GB versus 650 MB).
The second type of DVD differs from the first type of DVD by the utilization of a second layer beneath the top layer on which additional data can be stored. A special coating is used on the first layer that allows the laser to access the data on the second layer. The two layer format offers up to 8.5 GB of data storage.
Unlike most uses of current CD-ROMs, it is contemplated that both sides of the DVD can and will ultimately be used to store data. When using both sides of a DVD having the two layer format there is potential for 17 GB of storage on a single disk. However, the initial DVDs anticipated to be introduced into the public will utilize the 4.7 GB format. As described above, because the data pits on DVDs are closer together than they are on conventional CD-ROMs, the initial DVD drives will offer data transfer rates of 1.35 MBps, which is equivalent to that of current 9.times. CD-ROM drives. This will be accomplished with a DVD drive having a spin rate about as fast a current 4.times. CD-ROM drives.
One of the highly anticipated applications for DVDs is in the Motion Picture industry. A full-length motion picture will be compressed onto a DVD using an algorithm known as MPEG-2 (Motion Pictures Experts Group). However, as with other forms of data storing media, such as current computer CD-ROMs and floppy disks, and laser disks and video tapes for movies, one of the main items of concern is the unauthorized copying and distribution of the data. This will be especially true with DVDs. Because the data is digitally stored on a DVD, copies of the DVD can be made without any degradation such that every copy of a DVD is indistinguishable from the original.
As can be appreciated, it is therefore highly desirable to have a copy-protection system for data recorded on various media, such as DVDs, that provides a high level of copy protection in a manner that is extremely difficult or prohibitively expensive and time consuming to defeat.